Deque Introduction
A deque (double-ended queue) is a generalized queue where you can insert and delete elements from both ends. It stands for "double-ended queue".
Deque supports operations:
- addFirst / offerFirst – insert at front
- addLast / offerLast – insert at rear
- removeFirst / pollFirst – remove from front
- removeLast / pollLast – remove from rear
- getFirst / peekFirst – examine front
- getLast / peekLast – examine rear
In Java, the `Deque` interface is part of the collections framework. `ArrayDeque` provides a resizable-array implementation and is usually faster than `LinkedList` for deque operations.
Example usage:
Deque deque = new ArrayDeque<>();
deque.addFirst(1); // front: 1
deque.addLast(2); // front: 1, rear: 2
deque.addFirst(0); // front: 0, then 1, then 2
System.out.println(deque.removeLast()); // 2
System.out.println(deque.removeFirst()); // 0
Two Minute Drill
- Deque allows insertion/removal from both ends.
- Supports both stack and queue operations.
- Java provides `ArrayDeque` and `LinkedList` implementations.
- Useful for sliding window problems, palindrome checking, etc.
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